Capacitor with buried isolated electrode

ABSTRACT

A capacitor includes a planar electrode layer which is mounted between a pair of dielectric layers. The electrode layer generally is placed slightly off-center with respect to the dielectric layers so that the electrode layer extends to an end portion of the dielectric layers. One layer of the pair of dielectric layers has a pair of spaced apart contact members, each having a different polarity from the other. The contact members extend onto end portions of the dielectric layers with one of the contact members forming an electrical connection with the electrode layer. The combination of the electrode layer, the dielectric layer on which the contact members are mounted, and the contact member not connected to the electrode layer, allow development of a selected value of capacitance. Providing trimmed contact members as well as controlling their size and spacing allow for convenient preselection of desired operative characteristics of the capacitor. The contact members could be positioned on a substrate to which a buried electrode is mounted.

CROSS-REFERENCE

[0001] The present application is a continuation-in-part of Applicant'sco-pending U.S. patent application Ser. No. 09/596673, filed Jun. 19,2000.

FIELD OF THE INVENTION

[0002] This invention relates generally to capacitors and moreparticularly to a ceramic capacitor which utilizes a buried layer.

BACKGROUND OF THE INVENTION

[0003] Prior art relating to solid state capacitors includes suchpatents as U.S. Pat. No. 4,665,465 to Tanabe and U.S. Pat. No. 5,107,394to Naito et al. Construction of these capacitors includes multipleelectrode layers which are fastened by means of soldering to amechanical end cap. A soldering process introduces a degree ofunreliability as a result of residual stresses formed in the capacitorduring its manufacture. Additional unreliability results from stresseswhich are imposed on a solder joint due to differential rates of thermalexpansion and contraction of various components of the capacitor;including its electrodes, its dielectric material, its solder materialand its end cap; when the capacitor is exposed to temperature variationsand extremes; with or without other stressful influences, during use.Also relevant is U.S. Pat. No. 5,576,926 to the present Applicant.

SUMMARY OF THE INVENTION

[0004] It is an object of the present invention to provide a buriedlayer capacitor that is particularly effective at very high frequencies.

[0005] Another object of the invention is to provide a buried layercapacitor which performs with highly reliability.

[0006] Another object of the invention is to provide a buried layercapacitor which is capable of highly reliability over a broad range ofoperating temperatures.

[0007] Yet another object of the invention is to provide a buried layercapacitor which can be manufactured in quantity at a low unit cost whilemaintaining high quality.

[0008] The foregoing and other objects and advantages of the inventionwill appear more clearly hereinafter.

[0009] In accordance with the invention, there is provided a buriedlayer capacitor which includes a planar electrode layer mounted betweena pair of dielectric layers. Length and width dimensions of thedielectric layers are somewhat greater than corresponding length andwidth dimensions of the electrode layer. The electrode layer is placedslightly off-center with respect to the dielectric layers so that theelectrode layer extends to an end portion of the dielectric layers. Onelayer of the pair of dielectric layers has a pair of spaced apartcontact members, each having a different polarity from the other. Thecontact members extend onto the end portions of the dielectric layerswith one of the contact members forming an electrical connection withthe electrode layer. The contact member design helps facilitate testingof the circuit. The combination of the electrode layer, the dielectriclayer on which the contact members are mounted, and the contact membernot connected to the electrode layer, allow development of a selectedvalue of capacitance.

[0010] In an alternative embodiment of the invention, the pair of spacedapart contact members is replaced by a pair of metallized areas eachhaving a different polarity from the other. The metallized areasfacilitate mounting the buried layer capacitor on a circuit board whileusing minimum surface area of the circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other important objects and advantages of the invention will beapparent from the following detailed description, taken in connectionwith an accompanying drawings in which:

[0012]FIG. 1 is a generally downwardly looking perspective view of aburied layer capacitor made in accordance with the present invention andhaving a portion of the capacitor shown broken away to reveal details ofinternal construction;

[0013]FIG. 2 is an elevational cross-sectional view taken along line2--2 of FIG. 1;

[0014]FIG. 3 is a planar cross-sectional view taken along line 3--3 ofFIG. 2;

[0015]FIG. 4 is an elevational cross-sectional view taken along the line4--4 of FIG. 1;

[0016]FIG. 5 is a side elevational view taken along the line 5--5 ofFIG. 1;

[0017]FIG. 6 is a generally downwardly looking perspective view of analternative embodiment of the buried layer capacitor of FIG. 1;

[0018]FIG. 7 is a bottom planar view of the capacitor of FIG. 6 takenalong the line 7--7 of FIG. 6;

[0019]FIG. 8 is a side elevational view of the capacitor of FIG. 6;

[0020]FIG. 9 is an end elevational view of the capacitor of FIG. 6;

[0021]FIG. 10 is a side elevational view of an alternative embodiment ofthe buried layer capacitor of FIG. 1, incorporating a pair of axialleads;

[0022]FIG. 11 is a bottom planar view of the capacitor of FIG. 10, takenalong line 11--11 of FIG. 10;

[0023]FIG. 12 is a side elevational view of another embodiment of theburied layer capacitor of FIG. 1, incorporating metallized portions,each having a different polarity from the other, on the end surfaces ofthe dielectric layers;

[0024]FIG. 13 is an end elevational view of the capacitor of FIG. 12;

[0025]FIG. 14 is a perspective view of the capacitor of FIG. 12;

[0026]FIG. 15 is a bottom planar view of another embodiment of theburied layer capacitor of FIG. 1, similar to FIG. 7 and incorporating asquare configuration;

[0027]FIG. 16 is an end elevational view of the capacitor of FIG. 15;and

[0028]FIG. 17 is a cross-sectional view of an exemplary capacitor.

DETAILED DESCRIPTION

[0029] With reference to the drawings, wherein like reference numbersdesignate like or corresponding parts throughout, there is shown in FIG.1 a buried layer capacitor generally designated 10, made in accordancewith the present invention, which includes an electrode layer 12, afirst dielectric layer 14, a second dielectric layer 16 and a pair ofcontact members 18, 20, each of the contact members having a differentpolarity from the other.

[0030] The dielectric layers 14, 16 preferably are rectangular and as isshown in FIGS. 1 and 3, the electrode layer 12 also is generallyrectangular, with length and width dimensions which are somewhat smallerthan corresponding length and width dimensions of the dielectric layers14, 16. The electrode layer 12 is planar and generally is centeredrelative to the dielectric layers 14, 16 resulting in a border,generally designated in FIG. 3 by the reference numeral 22, whichsurrounds a periphery of the electrode layer 12. The electrode layer 12thus is completely contained or buried in the dielectric layers 14, 16.The electrode layer may be silver, gold, nickel, copper, palladium oranother high conductivity metal.

[0031] The contacts members 18, 20 are shown attached to a bottomsurface 24 of the dielectric layer 14. The contacts members 18, 20preferably are each planar and are made of any one of a number of metalswhich have desirable combination of stiffness and conductivity.Appropriate materials for the contact members are copper and silver.

[0032] The dielectric layers 14, 16 are made of any one of a number ofdielectric materials such as magnesium titanate, strontium titanate orbarium titanate.

[0033] As is best seen from FIG. 1, the first dielectric layer 14 isdisposed between the electrode layer 12 and the contacts members 18, 20.The contacts members 18, 20 have a preferred thickness which is in theorder of 0.01 inches. The dielectric layer 14, in combination with theelectrode layer 12 and the contacts members 18, 20, (each having adifferent polarity from the other) allow development of capacitancebetween the contacts members 18, 20.

[0034] The buried layer capacitor 10 of FIGS. 1-5 typically has thefollowing dimensions which should be considered as given by way ofillustration only and should not be considered as limiting in any way.Overall length of the capacitor 10 is in an order of 0.05 inches, itswidth is in an order of 0.05 inches, its height is in an order of 0.02inches. Thickness of the dielectric layer 14 is in an order of 0.003inches and thickness of the dielectric layer 16 is in an order of 0.017inches.

[0035] The thickness of the dielectric layer 14 typically may range from0.0005 inches to 0.01 inches in order to vary capacitance and thevoltage rating of the capacitor 10.

[0036] The dimensions of the electrode layer 12 are typically asfollows: length 0.045 inches, width 0.045 inches, and thickness 0.0001inches.

[0037] An alternative embodiment of a capacitor generally designated 100according to the invention is shown in FIGS. 6-9. In the capacitorembodiment 100, the contact members 18, 20 are replaced by a pair ofmetallized areas 102, 104 on a bottom surface 106 of the capacitor asshown in FIG. 8. The metallized areas 102, 104 function as terminations,each having a different polarity from the other, and facilitate mountingof the capacitor 100 directly to a printed circuit board. Elimination ofthe contacts members 18, 20 results in use of a minimum amount ofcircuit board area for the capacitor 100.

[0038] The capacitor 100 includes a first dielectric layer 14 and asecond dielectric layer 16 and an electrode layer 12, each of which isgenerally similar to corresponding parts which have been described inconnection with the embodiment depicted in FIGS. 1-5.

[0039] The capacitor 100 typically includes an electrode layer 12 madeof palladium and metallized areas 102, 104 or terminals made of silver.

[0040] The following physical dimensions and capacitance values for theburied layer capacitor 100 should be considered as given by way ofexample and should not be considered as limiting in any way. The lengthdimension (as measured along edge 106) may range from 0.040 inches to0.50 inches; the width (as measured along edge 108) may range from 0.020inches to 0.50 inches; and the thickness (as measured along edge 110)may range from 0.010 to 0.10 inches.

[0041] Most typically, the capacitor 100 is manufactured in thefollowing sizes: TABLE 1 Typical Capacitor Sizes LENGTH WIDTH THICKNESSSIZE (inches) (inches) (inches) A 0.060 0.050 0.030 B 0.120 0.100 0.080

[0042] The margin or barrier at the sides and at the ends of theelectrode layer 12 as indicated by the reference numeral 112 in FIG. 7may range from 0.005 inches to 0.010 inches. The gap between theterminations 102, 104 as indicated by the reference numeral 114 in FIGS.6, 7 and 8 may range from 0.005 inches to 0.020 inches. The thickness ofthe dielectric layer 14 between the electrode layer 12 and theterminations 102, 104 may range from less than 0.001 inches to 0.010inches.

[0043] In another alternative configuration generally designated 200shown in FIG. 15, the length and width dimensions are made equal,thereby resulting in a the square configuration of the buried layercapacitor 200.

[0044] Typical values for capacitance for a buried layer capacitor 100having a size designated as Size A in Table 1 for various values ofdielectric thickness, margin size, gap spacing and dielectric constantare shown in Table 2. The capacitance values shown are in pico Farads(pF) as measured between terminations 102, 104. TABLE 2 CapacitanceValues for Buried Layer Capacitors DIELECTRIC THICKNESS MARGIN GAPDIELECTRIC CONSTANT (inches) (inches) (inches) K = 13 K = 23 K = 65 K =90 K = 4000 0.001 0.005 0.010 1.1 pF 2.3 pF 5.7 pF 7.8 pF 351 pF 0.0100.005 0.010 0.1 pF 0.4 pF 0.001 0.010 0.010 0.4 pF

[0045] An important feature of the buried layer capacitor 100 is theability to adjust or trim the value of capacitance in an efficientmanner. The capacitance of the buried layer capacitor 100 can beadjusted by adjusting the gap 114 between the terminations 102, 104 eachhaving a different polarity from the other. Such adjustment may beperformed as a final part of a manufacturing process and eliminates needfor contacting and trimming the electrode layer 12. This adjustment maybe accomplished by trimming or cutting away a small portion of theterminations along the edges 116, 118 using conventional abrasioncutting or laser cutting equipment.

[0046]FIGS. 10 and 11 show an alternative embodiment of the buried layercapacitor contacts members 300 which incorporates axial contact members302, 304. The axial contacts members 302, 304 provide an alternativemounting configuration.

[0047] FIGS. 12-14 show another alternate embodiment of the buried layercapacitor generally designated 400 in which the metallized areas 102,104 or cathode and anode shown in FIG. 6 have been modified to extendonto the end surfaces 402, 404 of the dielectric layers 14, 16. Theterminations 406, 408 on the buried layer capacitor 400 facilitate useof test equipment in which probes are placed on surfaces 410, 412 inorder to measure performance characteristics of the capacitor 400.

[0048]FIG. 17 shows an exemplary embodiment of the buried layercapacitor generally designated 500 in which the electrode layer 12 isextended through dielectric layers 14, 16 to electrically connect to thetermination 408. This connection shorts the capacitor defined theelectrode layer 12, the dielectric layer 14, and the termination 408.Prior to the shorting, that capacitor was in a series connection withthe capacitor defined by the electrode layer 12, the dielectric layer14, and the termination 406. If a first capacitor is defined with acapacitance of C1 and a second capacitor is defined with a capacitanceof C2 and the first and second capacitors are in a series connection,the equivalent capacitance is equal to C1 times C2 divided by the sum ofC1 plus C2. If C1 equals C2, then the equivalent capacitance is equal to½ of C1 or C2, because they are of the same value. Thus, shorting one ofthe two series capacitors, as seen in FIG. 17, has the net effect ofdoubling the capacitance. The buried layer capacitor 500 functions thesame mechanically and electrically as the buried layer capacitorsgenerally designated 10, 100, 200, 300, 400, respectively, albeit withtwice the capacitance.

[0049] In a preferred embodiment of the buried layer capacitor 500, theterminations 406, 408 extend along end surfaces 402, 404. Thisarrangement provides additional surface area for bonding and simplifiesinspection and connection to the circuit board.

[0050] The relatively thicker dielectric layer 16 contributes to overallruggedness of the buried layer capacitors generally designated 10, 100,200, 300, 400, 500, respectively thicker dielectric layer 16. Thisrelatively thicker dielectric layer 16 makes it possible to handle thesecapacitors using conventional production type automatic handlingequipment, even though the dielectric layer 14 is in the range of 0.0001inches to 0.01 inches.

[0051] A key feature of the buried layer capacitors generally designate10, 100, 200, 300, 400, 500, respectively is their performances at veryhigh frequencies. A typical capacitor made according to the prior art isuseful up to approximately 11 gigaHertz (11 GHz). Tests performed oncapacitors made according to the present invention indicate usefulperformance to 20 GHz and above.

[0052] The foregoing specific embodiments of the present invention asset forth in the specification herein are for illustrative purposesonly. Various deviations and modifications may be made within the spiritand scope of this invention, without departing from a main themethereof.

What is claimed:
 1. A buried layer capacitor comprising: a firstdielectric layer, with said first dielectric layer having a lengthdimension and a width dimension, and with said first dielectric layerhaving a first surface and a second surface; an electrode layer, withsaid electrode layer having a length dimension and a width dimension,with said length and width dimensions of said electrode layer smallerthan said length and width dimensions respectively of said firstdielectric layer, and with said electrode layer mounted on said firstsurface of said first dielectric layer, spaced from contact with anyelectrical conductor; a second dielectric layer, with said seconddielectric layer having a length dimension and a width dimension andwith said length and width dimensions of said second dielectric layercoextensive with said length and width dimensions respectively of saidfirst dielectric layer; two spaced apart contact members with saidcontact members in contact with said second surface of said firstdielectric layer, each of said contact members provided with a differentpolarity from that of said other contact member, and with each of saidcontact members extending onto an end surface of said first and saidsecond dielectric layers.
 2. A buried layer capacitor according to claim1, wherein said electrode layer extends outwardly to contact one of saidcontact members.
 3. A buried layer capacitor according to claim 2, inwhich said electrode layer is rectangular.
 4. A buried layer capacitoraccording to claim 2, in which said first and said second dielectriclayers are each rectangular.
 5. A buried layer capacitor according toclaim 2, in which each of said contact members projects beyond saidwidth dimension of said first dielectric layer.
 6. A buried layercapacitor according to claim 2, in which said electrode layer is square.7. A buried layer capacitor according to claim 2, in which said firstand said second dielectric layers are each square.
 8. A method forproducing a capacitor and comprising steps of: providing a first thindielectric layer having a length dimension and a width dimension and afirst surface and a second surface; providing an electrode layer withlength and width dimensions smaller respectively than those of saidfirst dielectric layer, the electrode layer mounted centrally on thefirst surface of the first dielectric layer with said electrode layerspaced from contact with any electrical conductor; providing a seconddielectric layer on the electrode layer on the opposite side from thefirst dielectric layer for ruggedness, the second dielectric layerhaving length and width dimensions coextensive with those of said firstdielectric layer so that said dielectric layers combine to describe amargin outward of the electrode layer; providing two spaced apartelectrical contact members in contact with the second surface of thefirst dielectric layer, each of said contact members being provided witha different polarity from that of said other contact member, and witheach of said contact members extending onto an end surface of said firstand said second dielectric layers.
 9. A buried layer capacitor accordingto claim 8, wherein said electrode layer extends outwardly to contactone of said contact members.
 10. A buried layer capacitor according toclaim 9, in which each of said pair of electrically conductive areas isrectangular.
 11. A buried layer capacitor according to claim 9, in whicheach of said electrically conductive areas comprises a metallized area.12. A buried layer capacitor according to claim 9, in which saidelectrode layer is rectangular.
 13. A buried layer capacitor accordingto claim 9, in which said first and second dielectric layers are eachrectangular.
 14. A buried layer capacitor according to claim 9, in whichsaid electrode layer is square.
 15. A buried layer capacitor accordingto claim 9, in which said first and said second dielectric layers areeach square.
 16. A method for producing a capacitor and comprising stepsof: providing a first thin dielectric layer having a length dimensionand a width dimension and a first surface and a second surface;providing an electrode layer with length and width dimensions smallerrespectively than those of said first dielectric layer, the electrodelayer mounted centrally on the top surface of the first dielectric layerwith said electrode layer spaced from contact with any electricalconductor; providing a second dielectric layer on the electrode layer onthe opposite side from the first dielectric layer for ruggedness, thesecond dielectric layer having length and width dimensions coextensivewith those of said first dielectric layer so that said dielectric layerscombine to describe a margin outward of the electrode layer; providingtwo trimmed spaced apart electrical contact members on the secondsurface of the first dielectric layer, each of said contact membersbeing provided with a different polarity from that of said other contactmember so as to provide predetermined operative characteristics to thecapacitor, and with each of said contact members extending onto an endsurface of said first and said second dielectric layers.
 17. A buriedlayer capacitor according to claim 16, wherein said electrode layerextends outwardly to contact one of said contact members.
 18. A methodfor producing a capacitor and comprising steps of: providing a firstthin dielectric layer having a length dimension and a width dimensionand a first surface and a second surface; providing an electrode layerwith length and width dimensions smaller respectively than those of saidfirst dielectric layer, the electrode layer mounted centrally on the topsurface of the first dielectric layer with said electrode layer spacedfrom contact with any electrical conductor; providing a seconddielectric layer on the electrode layer on the opposite side from thefirst dielectric layer for ruggedness, the second dielectric layerhaving length and width dimensions coextensive with those of said firstdielectric layer so that said dielectric layers combine to describe amargin outward of the electrode layer; providing two spaced apartelectrical contact members on the second surface of the first dielectriclayer, each of said contact members being provided with a differentpolarity from that of said other contact member, the contact memberssized and spaced so as to provide predetermined operativecharacteristics to the capacitor, and with each of said contact membersextending onto an end surface of said first and said second dielectriclayers.
 19. A buried layer capacitor according to claim 18, wherein saidelectrode layer extends outwardly to contact one of said contactmembers.